Ink jet printers employ a multi-orifice print head for ejecting ink drops onto a print medium such as paper. An acoustic driver, such as a piezoelectric transducer, is coupled to a diaphragm for ejecting ink drops from an ink chamber, through a nozzle orifice, and onto a print medium. A control signal, provided by a signal source, is applied to the transducer and the diaphragm is displaced according to the voltage of the control signal. A typical signal source provides a positive pulse which lasts for some period of time and then returns to zero volts. The signal remains at zero volts for some period of time and is then followed by a negative pulse which lasts for a period of time and then returns to zero volts. During the positive pulse, the piezoelectric transducer displaces the diaphragm away from the cavity interior and ink from the reservoir is drawn into the cavity. In response to the negative pulse, the diaphragm is displaced, compressing the cavity and an ink drop is ejected from the orifice onto the print medium.
Solid ink piezoelectric transducers require on the order of plus and minus 50 volt waveforms. A common waveform generator is typically used for all jets of a print head. When a particular ink jet is to fire an ink drop, individual electronic switches (which are typically high voltage FETs) connect the waveform to that ink jet. These switches have the ability to disconnect part way through the leading edge of each waveform pulse in order to control the voltage to the jet transducer. The intrinsic load capacitance of the piezoelectric element holds the voltage at the time of disconnect, the switches and load capacitance operating analogous to a “track and hold” network. In a multi-orifice print head, not all of the ink jets produce droplets of the same size or consistency. U.S. Pat. No. 5,502,468, Ink Jet Print Head Drive with Normalization, describes a process for normalizing the ink jets in which voltage adjustment is used to normalize the performance of all the jets within a print head. For each ink jet, the voltage applied during each positive and negative cycle is varied by varying the time of the disconnect in order to ensure that each resulting ink drop has the same size and consistency.
Control logic signals, which are low voltage level signals on the order of 3.3 volts to 5 volts depending on the control logic circuitry, determine which ink jets will print at which time. A voltage level shifter or translator takes the low voltage control logic signals and translates them into the high voltage signals needed to drive the FET switches used to activate the piezoelectric transducers. Many voltage level translators exist. Typical ink jet print head voltage level translator/drivers use P-channel FETs to connect the jets to the positive waveform generator. N-channel FETs are much smaller and generally less expensive for given performance, but are more difficult to drive for high side switching. An important objective of any voltage level translator is the reduction in the time required to translate an input signal to an output signal. Ink jet print head level translator/drivers using P-channel FETs require up to 400 ns to change state. Faster printers typically need 75 ns or less.